i486 A MANUAL OF ANATOMY 



round the outer aspect of the cms cerebri, between which and the 

 temporal lobe it makes its superficial appearance. 



The fourth nerve supplies the superior oblique muscle of the 

 eyeball. 



Fifth Cranial, Trigeminal, or Trifacial Nerve. — The fifth cranial 

 nerve resembles a spinal nerve in having two roots — sensory and 

 motor — ^the former being large, and having a ganglion, called the 

 Gasserian ganglion. 



Sensory Root. — ^The fibres of this root are derived from the 

 central poles of the bipolar cells of the Gasserian ganglion. After 

 entering the pons Varolii each fibre divides into two branches — 

 ascending and descending, as in the case of the fibres of the dorsal 

 ■or sensory root of a spinal nerve. The terminal nuclei of these 

 ascending and descending sensory fibres are two in number — ^upper 

 and lower. 



The upper sensory nucleus is situated in the outer portion of the 

 dorsal part of the pons Varolii, where it lies close to the outer side 

 of the pontine or principal motor nucleus of the nerve. The 

 ascending sensory fibres, after a short course, enter this nucleus and 

 terminate in arborizations around its cells. 



The lower sensory nucleus, which is a continuation of the upper 

 sensory nucleus, is an upward prolongation of the substantia 

 gelatinosa of Rolando from the tubercle and funiculus of Rolando in 

 the medulla oblongata. The nucleus is traceable as low as the 

 dorsal grey cornu of the spinal cord on a level with the second 

 cervical spinal nerve, where it is close to the substantia gelatinosa 

 of Rolando. The descending sersory fibres, which are numerous 

 and constitute the spinal or descending sensory root of the fifth nerve, 

 pass downwards through the pons and medulla oblongata into the 

 spinal cord, as low as the level of the second cervical spinal nerve. 

 They are accompanied by the lower sensory nucleus, and at different 

 levels they enter this nucleus and terminate in arborizations around 

 its cells. 



The most of the axons of the cells of the terminal sensory nuclei 

 pass inwards to the raphe and cross to the opposite side. They then 

 become longitudinal and ascend in company with the mesial fillet 

 or chief sensory tract, their destination being the optic thalamus 

 of the side to which they have crossed. They thus constitute a 

 trigemino-thalamic ascending tract. From these fibres collaterals are 

 furnished to (i) the facial nucleus, and (2) the ventral vago-glosso- 

 pharyngeal nucleus, or nucleus ambiguus, from the cells of which 

 latter the efferent or motor fibres of the pneumogastric or vagus 

 nerve arise. 



A few of the axons, however, enter the pontine or chief motor 

 nucleus, and also the mesencephalic or accessory motor nucleus, of 

 the nerve, and terminate in arborizations around its cells. 



Motor Root. — ^The fibres of this small root are derived from two 

 nuclei — pontine and mesencephalic. 



The pontine or chief motor nucleus is situated in the outer portion 



